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Using Six Monitors With AMD's Open-Source Linux Driver

05-19-2013, 02:50 PM

Phoronix: Using Six Monitors With AMD's Open-Source Linux Driver

Linux graphics drivers have come a long way in recent years for both the open and closed-source solutions from AMD, NVIDIA, and Intel. In this Sunday article, a Phoronix reader has shared his experiences in going from failing to setup two monitors under Linux just a few years ago with NVIDIA to now successfully driving six monitors on a single system using the AMD Linux driver...

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Linux graphics drivers have come a long way in recent years for both the open and closed-source solutions from AMD, NVIDIA, and Intel. In this Sunday article, a Phoronix reader has shared his experiences in going from failing to setup two monitors under Linux just a few years ago with NVIDIA to now successfully driving six monitors on a single system using the AMD Linux driver...

Comment

AMD hardware only has two non-DP (DisplayPort) PLLs. Officially this means that only two non-DP monitors are supported. If you want to use more than two monitors, the rest of them should be native DP (or using active DP adapters). Technically this setup is not officially supported. That said, I added support for sharing non-DP PLLs in kernel 3.7 which means that you can share PLLs between non-DP displays if the selected modes on the displays share the same display clock. That's probably what "fixed" it, but it has some limitations and it wasn't really a bug per se.

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I am running three monitor setup with my Sapphire HD6850 for quite some time. 3 Samsung 20" SyncMaster 204B/BM moniotrs, with each 1600x1200 = 4800x1200
Two monitors are on DVI port and third is conneted through active Displayport to DVI interface.

It works very well on open source radeon driver.

For my next setup I plan to use FPGA to drive multiple LCD panels from Displayport directly.

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I am running three monitor setup with my Sapphire HD6850 for quite some time. 3 Samsung 20" SyncMaster 204B/BM moniotrs, with each 1600x1200 = 4800x1200
Two monitors are on DVI port and third is conneted through active Displayport to DVI interface.

It works very well on open source radeon driver.

For my next setup I plan to use FPGA to drive multiple LCD panels from Displayport directly.

I think this article was more about the fact that just 6months ago...you shouldnt have even TRIED this. And now its working out of the box no problems.

Comment

AMD hardware only has two non-DP (DisplayPort) PLLs. Officially this means that only two non-DP monitors are supported. If you want to use more than two monitors, the rest of them should be native DP (or using active DP adapters). Technically this setup is not officially supported. That said, I added support for sharing non-DP PLLs in kernel 3.7 which means that you can share PLLs between non-DP displays if the selected modes on the displays share the same display clock. That's probably what "fixed" it, but it has some limitations and it wasn't really a bug per se.

Could you elaborate on that ? Up untl now I thought the bottleneck is in framing circuits, since each frame is just a packet on Displayport while it has to be framed on other outputs ( X pixels in a row in Y rows with certain bit organisation within pixel and timings so it reaches the "phosphor" at exactly right moment).

Your post implies that actually good PLL is expensive part wrt to silicon area and that ATI has been skimping on PLLs, not framing circuits.

If so, it would be nice to know how could one drive M identical monitors at identical framerate and resolution with one PLL.

Had I known how to do it before, it would spare me from much of the headscratching, endless googling, many failed attempts with passive adapters ( basically just a piece of wire and two connectors), suffering with DP-VGA adapter and using the latest addition XFX DP-DVI active adapter.

Active adapters are not that cheap and adapters for dual-link DVI are outrageously expensive...

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Setup on last photo was probably with closed source driver, but it did not take me long to switch to open-sauce radeon.

It was a week or so sifting through the net like mad until I've got a hang of it. I remember having to got IRC channel #radeon for advice that finally enabled me to unlock that lock.

I've ended up on open driver, since it was updated much more frequently and developers reacted to user gripes with some energy. At the time closed driver ahd a nasty bug whic caused cursor corruption in certain situations, so I used radeon kernel module and xf86-video-ati open-source combination.